Method and assembly for water filtration using a tube manifold to minimize backwash

ABSTRACT

A method of filtering a feed liquid in a membrane filtration assembly is provided comprising introducing feed liquid to be treated into a filtration chamber of a membrane filtration system including a membrane module having one or more permeable hollow membranes, the module being located in the filtration chamber, and the filtration chamber having an open upper end located above an upper header of the membrane module and a closed lower end, and feed tank surrounding the filtration chamber. The feed tank may be configured to provide the feed liquid through the open upper end of the filtration chamber, and the feed liquid may be applied to the surface of the membranes within the membrane module and withdrawn from the lumens of the membranes as filtrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §120 as a divisionof U.S. patent application Ser. No. 12/064,409 filed on Feb. 21, 2008,titled “ASSEMBLY FOR WATER FILTRATION USING A TUBE MANIFOLD TO MINIMISEBACKWASH,” which is a U.S. national stage application that claimspriority under 35 U.S.C. §371 to International Application No.PCT/AU2006/001215 filed on Aug. 22, 2006, titled “AN ASSEMBLY FOR WATERFILTRATION USING A TUBE MANIFOLD TO MINIMISE BACKWASH,” that claimspriority to Australian Provisional Application Serial No. 2005904552,titled “AN ASSEMBLY FOR WATER FILTRATION USING A TUBE MANIFOLD TOMINIMISE BACKWASH,” filed Aug. 22, 2005, each of which is hereinincorporated by reference in their entirety for all purposes.

TECHNICAL FIELD

The present invention relates to membrane filtration systems and methodsand, more particularly, to a system and method that allows forfiltration under gravity, under pressure or using a high feed head whileminimizing the backwash and cleaning solution volume.

BACKGROUND OF THE INVENTION

In a membrane filtration operation, periodically cleaning the membraneby liquid or gas backwash is essential to keep a longer membraneoperation time without the need for a chemical cleaning stage. However,during each backwash, a certain amount of liquid waste is produced,which reduces the feed liquid recovery and increases the requirements onpost treatment of backwash is waste. The liquid or gas backwash is alsosupplemented by periodic cleaning of the membranes using a chemicalcleaning agent. This process again produces liquid waste which must befurther treated or disposed of in an environmentally safe manner. It isthus desirable in any filtration operation to minimize the volume ofwaste liquid produced during the backwash and chemical cleaning phasesof operation in order to reduce costs of operation and any environmentalimpact.

SUMMARY OF THE INVENTION

According one aspect the present invention provides a membranefiltration assembly including:

a membrane module having one or more permeable hollow membranessupported therein by at least one header, a filtrate collection chamberassociated with said header and in fluid communication with lumens ofsaid membranes for collecting filtrate withdrawn through said membranelumens;

a filtration chamber for receiving feed liquid to be applied to thesurface of membranes within said module, said filtration chamberenclosing said module and extending beyond the height of said module.

Preferably, the membranes extend between a pair of spaced, opposedheaders. For preference, a filtrate collection chamber is associatedwith one or both of said headers. Preferably, said membranes arepositioned vertically within said module and said headers are respectiveupper and lower headers. For preference, a filtrate carrier is providedbetween and in fluid communication with said filtrate collectionchambers. Preferably, said filtrate carrier extends through said modulebetween said headers. For preference, an opening or openings areprovided in the upper header to allow the flow of fluid therethrough.

In one embodiment, said filtration chamber is closed at one end and openthe other. In another embodiment, the open end of the filtration chamberis provided with a valve which allows gas flow therethrough while onlyallowing liquid flow into the filtration chamber,

Preferably, the region defined between the filtration chamber and themodule is filled with one or more filler elements. For preference anaeration backwash device is provided in fluid communication with saidfiltration chamber for selectively communicating gas and/or liquid toand/or from said filtration chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 shows a schematic sectional elevation view of a filtration moduleaccording to one embodiment of the invention;

FIG. 2 shows a schematic sectional elevation view of the filtrationassembly according to one embodiment of the invention operating in agravity suction mode;

FIG. 3 shows a schematic sectional elevation view of the filtrationassembly according to one embodiment of the invention operating in apressurized mode; and

FIG. 4 shows a schematic sectional elevation view of the filtrationassembly according to one embodiment of the invention operating in ahigh head mode.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, the membrane filtration module 5 according to onepreferred embodiment consists of a bundle of hollow fiber membranes 6potted at the top and bottom in upper and lower headers 7 and 8respectively to expose the fiber membrane lumens to collect filtrate. Itwill be appreciated the fiber bundle may be potted at either or bothends, and further that the fiber lumens may be open at either or bothends. An opening or openings may be provided in the upper header toallow the flow of fluid therethrough.

A filtrate carrier 9 (typically a pipe or tube) extends between theupper and lower headers 7 and 8 to allow filtrate to be collected fromeither or both ends of the fiber membrane lumens. The carrier 9 may beof any shape in cross section and, though shown in this embodiment inthe centre of the module 5, it may be located anywhere in the pot and insome embodiments the filtrate carrier 9 need not be located in themodule 5 but can be connected through external connections as describedbelow.

Referring to FIGS. 2 to 4, the filtration assembly 10, according to apreferred embodiment of the invention, consists of a filtration chamber11 higher than the module 5. If used in the high head filtration mode,as shown in FIG. 4, the filtration chamber 11 may be significantlyhigher than the module 5. The cross section of the filtration chamber UKpreferably resembles the cross section of the module 5, however, whenspacer fillers 12 are used, any cross section of the module may beaccommodated. The filtration chamber 11 may be integrally formed as onepiece or comprise multiple elements. The filtration chamber 11preferably has a constant cross-section along its length, however, itmay consist of multiple sections with a thicker cross section towardsits base.

A spacer filler 12 with an exterior cross section closely resembling thecross section of the filtration chamber 11 and an internal cross sectionclosely resembling the cross section of the module 5 is provided betweenthe module 5 and the filtration chamber 11. The spacer filler 12 is notessential to the operation of the filtration assembly 10 but in thepreferred embodiments is used to further reduce backwash and cleaningsolution volumes. The spacer filler 12 may be formed from a single ormultiple components.

A cap 13 is fitted to one end 14 of the module 5 to allow filtrate flow15 from the end of the module 5 into the filtrate carrier 9.

A module mounting piece 16 is sealingly attached to lower end of thefiltration chamber 11. The mounting piece 16 includes an aerationbackwash device 17 and a filtrate collection chamber 18.

As indicated above, the filtrate carrier 9 need not be located withinthe module 5. Instead, external connections between the cap 13 and thefiltrate collection chamber 18 or downstream thereof may be provided toallow for the collection of filtrate from the capped end of the module5.

The aeration/backwash device 17, at least in part, surrounds a portionof the membrane module 5 above the lower header 8. The aeration/backwashto device 17 includes a communication chamber 19 having upper and lowerthrough-openings 20 and 21 in fluid communication with the communicationchamber 19 and the membrane module 5. It will be appreciated howeverthat the function of the upper and lower through-openings may beperformed by one or more elongate openings which are, preferably,varying in width and, more is preferably, are wider at the lower endthan at the upper end. The communication chamber 19 is connected via apipe 22 to a feed, aeration, backwash and draindown header 23. Thecommunication chamber 19 in this embodiment is in the form of annulus 24which provides for the selective aeration, feed and backwash withthrough-openings 20 and 21 in the inner wall 25 of the annulus 24 toallow the flow of gas, feed liquid, backwash liquid into the module 5and draindown of waste liquid from the module 5. The annulus 24 mayfully or partially surround the membrane module 5.

It will be appreciated that the functions of the module mounting piece16 may provided by a single component or by multiple components.

A filtrate header 26 connects the filtrate collection chamber 18 frommultiple modules together to a common outlet (not shown).

The aeration, feed, backwash and draindown header 23 connects theaeration gas, feed liquid, backwash and draindown liquids from multiplemodules together to a common inlet/outlet (not shown).

Various modes of operation of this embodiment of the invention will nowbe described, by way of example only, with reference to FIGS. 2 to 4 ofthe drawings, respectively,

Gravity Suction Mode Operation

This mode of operation is illustrated in FIG. 2 of the drawings whichshows the filtration assembly 10 located in a feed tank 28. Although,the assembly 33 is shown located in a tank 28, it will be appreciatedthat the tank 28 is merely one means of providing feed liquid to thefiltration chamber 11 and other means such as pumping, flowing liquidfrom above and the like are equally applicable.

Filtration

The feed liquid level 29 in the surrounding feed tank 28 is raisedhigher than the filtration chamber 11 allowing feed liquid 30 to flowinto the filtration chamber 11. Feed liquid may also be pumped throughthe aeration, feed, drain down and backwash header 23 and suction may beapplied to the filtrate header 26. Significant pressure can beintroduced by high feed levels in the feed tank 28.

The feed liquid flows down the filtration chamber 11 and is divertedinto the module 5 by the spacer filler 12. The feed liquid is thenfiltered through the membranes 6 located in the module 5 and filtrate isrecovered from the ends of the module 5. Filtrate from the capped end 31of the module 5 flows through the filtrate carrier 9 to the bottom end32 of the module 5 and into the filtrate header 26.

Aeration

During the aeration step, the feed liquid level 29 is lowered in thesurrounding tank 28 to lower than the top of the filtration chamber 11.Gas, typically air, is then introduced through the aeration, feed, draindown and backwash header 23 to aerate the membrane module 5. The gasflows into the communication chamber 19 and is directed into themembrane module 5 through the aeration holes 20 in the module mountingpiece 16. The gas forms bubbles which scrub the membrane surfaces asthey rise through the module 5. The feed liquid level in the filtrationchamber 11 is arranged such that, during aeration, no feed liquid isable to escape from the filtration chamber 11 into the feed liquid inthe surrounding tank 28.

Feed Backwash

During the feed backwash process, the feed liquid level 29 is lowered inthe surrounding tank 28 to lower than the top of the filtration chamberBackwash liquid is then introduced through the aeration, feed, draindown and backwash header 23. The backwash liquid flows into thecommunication chamber 19 and is directed into the membrane module 5through the feed backwash holes 21 in the module mounting piece 16. Thebackwash liquid then scrubs the membrane surfaces as it rises throughthe module 5. The feed liquid level 29 in the filtration chamber 11 isarranged such that, during backwash, no feed liquid is able to escapefrom the filtration chamber 11 into the feed liquid in the surroundingtank 28.

In an alternative feed backwash process, backwash feed liquid isintroduced into the filtration chamber by raising the feed level 29 inthe tank 28 such that it overflows into the filtration chamber. Thebackwash liquid flows through the module 5 and out through the aeration,feed, drain down and backwash header 23. Suction may be applied to thebackwash header.

Permeate Backwash

During the permeate backwash process, the feed liquid level 29 islowered in the surrounding tank to lower than the top of the filtrationchamber 11. Feed is drained from inside the filtration chamber 11 andpermeate is introduced through pressurizing the filtrate header 26 withpermeate. The permeate backwash liquid flows through into lumens and outthrough the walls of the fibers removing solids from the surfaces of thefibers. During this step, permeate backwash liquid and solids may bedrained through the communication chamber 19 and into the aeration,feed, drain down and backwash header. The rate of introduction of thepermeate backwash liquid is arranged such that, during permeatebackwash, no permeate backwash liquid is able to escape from thefiltration chamber 11 into the feed liquid surrounding the tank 28.

Drain Down

After either or both of aeration and backwash the liquid and solids inthe filtration chamber 11 are drained out through the holes 20 and 21 inthe module mounting piece 16 into the aeration, feed, drain down andbackwash header 23.

Pressurized Mode Operation

As shown in FIG. 3, for operation in pressurized mode, an assembly 33 isprovided on the top end of the filtration chamber 11 that allows liquidto flow only into the filtration chamber 11 but not out thereof andallows gas to flow in both directions. In this embodiment, the assembly33 consists of a sealing cone 34 which seals onto the open end 35 of thefiltration chamber 11 with an opening 36 therein which is smaller than asealing ball 37. The sealing ball 37, which has an effective densityless than the feed liquid, is located and moves freely within thefiltration chamber 11.

It will be appreciated by those in the art that a variety of valvearrangements can be used to achieve the required function.

Although, the assembly 33 is shown located in a tank 28, it will beappreciated that the tank 28 is merely one means of providing feedliquid to the filtration chamber 11 and other means such as pumping,flowing liquid from above and the like are equally applicable.

Filtration

During filtration, the feed liquid is introduced to the filtrationchamber 11 through the aeration, drain down and backwash header 23, andsuction may be is applied to the filtrate header 26. As the level of thefeed liquid in the filtration chamber 11 is raised the sealing ball 37floats up to seal against the sealing cone 34 and closing opening 36,thereby allowing the filtration chamber 11 to be pressurized.

The feed liquid is then filtered through the membranes 6 in the module 5and filtrate is recovered from the ends of the module 5. Filtrate fromthe capped end 31 of the module 5 flows through the filtrate carrier 9to the bottom end 32 of the module 5 and into the filtrate header 26.

Aeration

During the aeration step, the feed liquid level 29 is lowered in thefiltration chamber 11, so that the sealing ball 37 is no longer incontact with the sealing cone 34 and the filtration chamber 11 isdepressurized. Gas is then introduced through the aeration, feed, draindown and backwash header 23. The gas flows into the communicationchamber 19 and is directed into the module 5 through the aeration holes20 in the module mounting piece 16. The gas forms bubbles which scourthe membrane surfaces as they rise through the module 5. The feed liquidlevel in the filtration chamber 11 is arranged such that, duringaeration, no feed liquid is able to escape from the filtration chamber11 into the feed liquid in the surrounding tank 28.

Feed Backwash

During the backwash process, the feed liquid level is lowered in thefiltration chamber 11, so that the sealing ball 37 is no longer incontact with the sealing cone 34 and the filtration chamber 11 isdepressurized. The feed liquid level in the surrounding tank 28 isarranged such that feed liquid overflows into the filtration chamber tobackwash the module. The backwash feed liquid flows is through themodule removing solids from the surfaces of the fibers. The backwashliquid drains through the aeration, feed, drain down and backwash header23. Suction may be applied to the backwash header.

Permeate Backwash

During the permeate backwash process, feed is drained from inside thefiltration chamber 11 and permeate is introduced through pressurizingthe filtrate header 26 with permeate. The permeate backwash liquid flowsthrough into lumens and out through the walls of the fibers removingsolids from the surfaces of the fibers. During this step, permeatebackwash liquid and solids may be drained through the communicationchamber 19 and into the aeration, feed, drain down and backwash header.The rate of introduction of the permeate backwash liquid is arrangedsuch that, during permeate backwash, no permeate backwash liquid is ableto escape from the filtration chamber 11 into the feed liquidsurrounding the tank 28.

Drain Down

After either or both of aeration and backwash the liquid and solids inthe filtration chamber 11 are drained out through the holes 20 and 21 inthe module mounting piece 16 into the aeration, feed, drain down andbackwash header 23.

High Head Mode Operation

As shown in FIG. 4, for high head mode operation the filtration chamber11 is extended significantly beyond the height of the module 5 suchthat, when the filtration chamber 11 is filled, a significant pressureis generated across the filtration surfaces of the membranes.

Filtration

During the filtration step, the feed liquid is introduced to thefiltration chamber 11, via the module 5, through the aeration, feed,drain down and backwash header 23, or directly into the filtrationchamber until the feed liquid level fills the filtration chamber 11.Suction may also be applied to the filtrate header 26.

The feed liquid is then filtered through the membranes 6 located in themodule 5 and filtrate is recovered from the ends of the module 5.Filtrate from the capped end 31 of the module 5 flows through thefiltrate carrier 9 to the bottom end 32 of the module 5 and into thefiltrate header 26. The feed liquid is introduced at such a rate thatthe level in the filtration chamber 11 stays within controlled limitsmaintaining sufficient pressure for filtration.

Aeration

Gas is introduced through the aeration, feed, drain down and backwashheader 23. The aeration gas flows into the communication chamber 19 andis directed into the module through the aeration holes 20 in the modulemounting piece 16. The gas forms bubbles which scour the surfaces of themembranes 6 as they rise though the module 5.

Feed Backwash

Backwash liquid is introduced through the aeration, feed, drain down andbackwash header 23. The backwash liquid flows into the communicationchamber 19 and is directed into the module 5 through the feed/backwashholes 21 in the module mounting piece 16. The backwash liquid scrubs thesurfaces of the membranes as it rises though the module 5.

Permeate Backwash

During the permeate backwash process, the feed liquid level 29 islowered in the surrounding tank 28 to lower than the top of thefiltration chamber 11. Feed is drained from inside the filtrationchamber 11 and permeate is introduced through pressurizing the filtrateheader 26 with permeate. The permeate backwash liquid flows through intothe lumens of the fibers 6 and out through the walls of the fibersremoving solids from the surfaces of the fibers. During this step,permeate backwash liquid and solids may be drained through thecommunication chamber 19 and into the aeration, feed, drain down andbackwash header.

Drain Down

After either or both of aeration and backwash the liquid and solids inthe filtration chamber 11 are drained out through the holes 20 and 21 inthe module mounting piece 16 into the aeration, feed, drain down andbackwash header 23.

It will be appreciated that the various backwashing processes and stepsdescribed above may be performed in a variety of combinations andsequences depending on the operating outcomes desired by the user.

It will be appreciated that further embodiments and exemplifications ofthe invention are possible without departing from the spirit or scope ofthe invention described.

What is claimed is:
 1. A method of treating a feed liquid, the methodcomprising: introducing the feed liquid to be treated into a filtrationchamber of a membrane filtration system including: a membrane modulehaving one or more permeable hollow membranes extending between an upperheader and a lower header of the membrane module, the membrane modulebeing located in the filtration chamber, the filtration chamber havingan open upper end located above the upper header of the membrane moduleand a closed lower end, and a feed tank surrounding the filtrationchamber and configured to provide the feed liquid through the open upperend of the filtration chamber; applying the feed liquid to surfaces ofthe one or more membranes within the membrane module; producing apressure differential across membrane walls of the one or moremembranes; filtering the feed liquid through the membrane walls intolumens of the one or more membranes as filtrate; and withdrawing thefiltrate from the lumens of the one or more membranes.
 2. The method ofclaim 1, further comprising providing feed liquid into the filtrationchamber by raising the level of the feed liquid within the feed tank toa level above the open upper end of the filtration chamber.
 3. Themethod of claim 1, further comprising flowing gas bubbles past thesurfaces of the one or more membranes to aerate the membranes within themembrane module.
 4. The method of claim 3, further comprising preventingliquid flow from the filtration chamber during aeration of the one ormore membranes.
 5. The method of claim 3, further comprising lowering alevel of the feed liquid within the feed tank to below a level below theopen upper end of the filtration chamber before aerating the one or moremembranes.
 6. The method of claim 1, further comprising flowing feedliquid past the surfaces of the one or more membranes to backwash themembranes within the membrane module.
 7. The method of claim 6, furthercomprising preventing liquid flow from the filtration chamber during thebackwashing of the one or more membranes.
 8. The method of claim 6,further comprising lowering the level of the feed liquid within the feedtank to a level below the open upper end of the filtration chamberbefore backwashing the one or more membranes.
 9. The method of claim 6,further comprising flowing the feed liquid out of the membrane modulethrough at least one opening in at least one of the upper and lowerheaders.
 10. The method of claim 6, further comprising raising a levelof the feed liquid within the feed tank to a level above the open upperend of the filtration chamber to cause the feed liquid to flow into thefiltration chamber before and/or during the backwashing of the one ormore membranes.
 11. The method of claim 1, further comprising performinga filtrate liquid backwash operation including: suspending filtering thefeed liquid through the membrane walls; flowing filtrate into the lumensand through the membrane walls to remove an accumulation of solids fromthe one or more membranes and form a backwash liquid containing removedaccumulated solids; and removing the backwash liquid containing theremoved accumulated solids from the filtration chamber.
 12. The methodof claim 11, further comprising: lowering a level of the feed liquidwithin the feed tank to a level below the open upper end of thefiltration chamber before performing a backwashing operation on the oneor more membranes; and arranging a rate of flow of filtrate backwashliquid into the filtrate chamber and a rate of removal of filtratebackwash liquid from the filtration chamber such that no filtratebackwash liquid flows from the filtration chamber into the feed tank.13. The method of claim 1, further comprising removing liquid from thefiltration chamber following at least one of aerating the one or moremembranes and backwashing the one or more membranes.
 14. A method offiltering a feed liquid, the method comprising: introducing the feedliquid into a filtration chamber of a membrane filtration systemincluding: a membrane module having one or more permeable hollowmembranes extending between an upper header and a lower header of themembrane module, the membrane module being located in the filtrationchamber, the filtration chamber having an open upper end located abovethe upper header of the membrane module and a closed lower end and afeed tank surrounding the filtration chamber and configured to providethe feed liquid through the open upper end of the filtration chamber;allowing a gas to flow into and out of the filtration chamber through avalve at the upper open end of the filtration chamber; providing thefeed liquid to the filtration chamber such that the valve at the upperopen end in the filtration chamber closes and prevents liquid flow outof the filtration chamber; applying the feed liquid to surfaces of theone or more membranes within the membrane module; pressurizing thefiltration chamber and producing a pressure differential across walls ofthe one or more membranes by continuing to provide the feed liquid tothe filtration chamber; filtering the feed liquid through walls of theone or more membranes into lumens of the membranes as filtrate; andwithdrawing the filtrate from the membrane lumens of the one or moremembranes.
 15. The method of claim 14, further comprising: opening thevalve to depressurize the filtration chamber; and flowing gas bubblespast the surfaces of the membranes to aerate the one or more membraneswithin the membrane module.
 16. The method of claim 14, furthercomprising performing a feed liquid backwash operation including:opening the valve to depressurize the filtration chamber; and flowingthe feed liquid past the surfaces of the one or more membranes tobackwash the one or more membranes within the membrane module.
 17. Themethod of claim 16, further comprising: opening the valve before a feedliquid backwashing operation begins by lowering a level of the feedliquid within the feed tank to a level below the open upper end of thefiltration chamber; and preventing liquid flow from the filtrationchamber into the feed tank during the feed liquid backwashing operation.18. The method of claim 14, further comprising performing a feed liquidbackwash operation including: opening the valve of the filtrationchamber to depressurize the filtration chamber and cause the feed liquidto flow into the filtration chamber lowering a level of the feed liquidwithin the feed tank while maintaining the level of the feed liquidabove the open upper end of the filtration chamber; and flowing the feedliquid within the filtration chamber past the surfaces of the one ormore membranes to backwash the one or more membranes within the membranemodule.
 19. The method of to claim 18, further comprising flowing thefeed liquid out of the membrane module through at least one opening inat least one of the upper and lower headers.
 20. The method of claim 14,further comprising performing a filtrate liquid backwash operationincluding: suspending filtering the feed liquid through the walls of theone or more membranes; flowing filtrate into the lumens of the membranesand through the walls of the membranes to remove an accumulation ofsolids from the one or more membranes and form a backwash liquidcontaining removed accumulated solids; and removing the backwash liquidcontaining the removed accumulated solids from the filtration chamber.21. The method of claim 20, further comprising: lowering the level ofthe feed liquid within the feed tank before the filtrate liquid backwashoperation to open the valve and depressurize the filtration chamber; andarranging a rate of flow of filtrate backwash liquid into the filtrationchamber and a rate of removal of filtrate backwash liquid from thefiltration chamber such that no filtrate liquid flows from thefiltration chamber into the feed tank.
 22. The method of claim 14,further comprising removing liquid from the filtration chamber followingat least one of an aeration operation and a backwash operation.